The present invention relates to a tunable gain coupled laser device with a laser waveguide with active material and a pumplaser which emits pumplight. The pumplight beams are oriented and directed towards the laser waveguide.
In gain guided (gain coupled) DFB-lasers (Distributed Feedback Laser) the laser frequency is given by the distance between two adjacent regions with a high gain of the material having to be half a wavelength in the waveguide. Up to now it has been difficult to make such devices tunable to specific frequencies within the gain region. One way is then to form a "grating" or similar with a period which can be varied, but such gratings are very difficult to realize, design etc. The advantages with obtaining a tunable gain coupled e.g. DFB-laser are considerable. It is well known that DFB-lasers generally are dynamically longitudinally mono-moded (single mode or mono-mode). Particularly gain coupled DFB-lasers are particularly mode-stable. It is also well known that optically pumped lasers have certain advantages such as for example that there are no requirements that the laser medium must have particular electrical properties, the laser resonator is not disturbed by electrical contacts and so on. The use of a laser as a pumplight source gives a good concentration of the pumping power but it is also quite complicated. In known arrangements it has furthermore been necessary to provide fixed reflection devices in the laser waveguide. In known tests, in pumping of lasers a standing wave pattern has unintentionally been created, i.e. a grating has been induced. The induced grating however did not correspond to the one that was intended with the laser resonator and in order to remove the grating, optical isolators have been introduced. In "Dye Lasers", 1973, pp. 78-82, F.P. Schafer an optically pumped DFB dye laser is described. This however merely relates to dye lasers which is very different from e.g. a semiconductor. It is thus not merely a matter of just changing active material. If e.g. a semiconductor is used as an active material, charge carrier diffusion must be prevented. Furthermore with the device in "Dye Lasers" reflection into the pumplaser will be caused and the device is not as compact as could be wanted.